Fuel cells are known to include collector plates such as bipolar or unipolar plates which serve to collect electrons generated from the consumption of fuel by the fuel cell and to deliver fuel cell reactant gases through reactant gas flow fields. These reactant gas flow fields are defined by one or more channels that have been machined, stamped, etched, molded or otherwise provided in a solid substrate which typically is made from a metal or composite material. The collector plates may be provided adjacent a diffusion media material which typically is a porous material such as carbon paper. Alternatively, in some arrangements, the collector plate may make direct contact to a catalytic electrode. Optionally, a microporous layer may underlie the gas diffusion media layer and a catalytic electrode may underlie the microporous layer or gas diffusion media layer. A polyelectrolyte membrane is provided underneath the first catalytic electrode and a second catalytic electrode is provided underlying a second face of the polyelectrolyte membrane. A second microporous layer may be provided underlying the second catalytic electrode and a second gas diffusion media layer underlying the second microporous layer or second catalytic electrode. A second collector plate is provided underlying the second gas diffusion media layer. The second collector plate also includes a reactant gas flow field defined by a plurality of channels and lands. The lands make physical contact with the gas diffusion media layer.
To facilitate water management in fuel cells, it is desirable to introduce hydrophilicity onto bipolar plate surfaces. Treating a bipolar plate surface to introduce surface hydrophilicity may be accomplished with an initial water contact angle no more than 15° (superhydrophilicity); with durability so that the water contact angle is stable enough not to exceed 15° throughout the life of the fuel cells; and the hydrophilic treatment does not adversely impact the contact resistance of the plates beyond an acceptable level.
Heretofore, silicon dioxide coatings have been used to selectively introduce hydrophilic characters to portions of bipolar plates. However, such and other organic based hydrophilic coatings suffer from: poor adhesion (under either wet or dry conditions) on substrates such as stainless steel; contamination due to the high surface energy of the superhydrophilic surface which is easily contaminated by less hydrophilic contaminants; dissolution, wherein the silicon dioxide can dissolve in the fuel cell environment via reaction with membrane degradation by products such as HF; thermal degradation, wherein coatings such as organic coatings age upon repeated exposure at temperatures of 90° and above and through repeated dry and wet cycles which lead to reorientation of hydrophilic groups on the top surface of such coatings, thus reducing the hydrophilicity thereof; electrochemical degradation, wherein certain hydrophilic groups in the substitution environment of a fuel cell can be electrochemically active and degrade.